This is Spinal Tap

Lumbar puncture (LP) , what lay people call a spinal tap, is a diagnostic test performed by ER docs rather frequently. The procedure is done to determine two potentially life threatening medical conditions: infections of the brain or the coverings of the brain which are called encephalitis and meningitis respectively, and subarachnoid hemorrhage (SAH), blood leaking from blood vessels on the surface on the brain. Headaches, fever, vomiting, confusion and lethargy may all be symptoms on these diseases.

Meningitis is an inflammation of the three membranes that cover the brain and spinal cord. Viruses, bacteria and occasional fungi and parasites may cause these infections. Non-infectious causes of meningitis include certain cancers. Encephalitis is an infection of the brain most commonly caused by viruses. West Nile, Eastern Equine and Herpes Simplex viruses are the most likely etiological agents.

Subarachnoid bleeding usually arises from arteriovenous malformation (AVM) or aneurysms in the circle of Willis. A SAH is suspected in any patient who presents to the ER with the "worst headache of their life". Thunderclap headaches come on suddenly, with severe pain at the onset of the headache. Even people with chronic headaches, such as migraines, who report that their presenting headache is different and more severe than usual, may have a SAH.

CT scans of the brain are done on any patient suspected of having a SAH. A scan may also be carried out on a patient who may have meningitis or encephalitis, if the physician thinks there may be a mass and/or increased pressure in the brain. Blood from a SAH shows up well on a CT. About 1% of SAH will not be visible on an initial CT. If the patient comes in days after their thunderclap headache, the CT may be normal as the density of the SAH may make it invisible on the CT. An LP will be done to insure that no case of SAH is missed.

This past month I did three LP's. The three patients ranged in age from 10 days to 30 years. The infant presented with a significant fever. All neonates (less than a month old) who have fever above a certain threshold must have an LP to check for meningitis. The other two LP's were on an adolescent with fever, headache, vomiting and neck stiffness (the classic symptoms of meningitis), and a patient with sudden onset of the worst headache of one's life with a CT that was negative for blood.

An LP may be performed with the patient sitting up and bending forward. More commonly the patient lies on his or her side, and curls into the fetal position. The skin is carefully cleansed with an antibiotic solution. The area is draped with sterile barriers and the ER doc wears sterile gloves and a mask. In my early days as an ER doc, the only way to ameliorate this painful test was with local anesthesia to numb the area. Luckily for my patients and for me, conscious sedation is now readily available. During the LP, a spinal needle enters the skin in the midline of the lower back. The target is between the 4th and 5th or 3rd and 4th lumbar vertebrae. The location of the LP is to prevent damage to the spinal cord. Having the patient bending forward or curled forward makes it easier to pass the spinal needle between the vertebrae. The needle is advanced until a faint "pop" is felt. The needle has now pierced the dura, the tough outermost covering of the central nervous system. The stylet in the spinal needle is removed and cerebral spinal fluid (CSF) begins to flow.

A manometer is sometimes attached to the spinal needle to measure the pressure of the CSF. 3-4 tubes of fluid are obtained, each containing about 1 milliliter of CSF. The pressure, color, and clarity of the CSF may all give clues as to the diagnosis. The CSF is sent to the lab to be analyzed for the presence and number of both red (RBC) and white (WBC) blood cells. The number of WBC's are further divided into the type of WBC. If a SAH is suspected, the RBC count is performed on the 1st and 4th tubes to see if the number is the same or changing. The CSF is cultured for microorganisms, and examined under a microscope after being stained with dyes. The glucose and protein of the CSF is measured. Additional tests may be ordered if unusual infections are suspected.

I now offer all my patients the option of having their LP done with conscious sedation (CS). The agreeable patient (written informed consent) is placed on continuous monitoring of their heart rate, oxygen saturation and blood pressure. The drugs used vary, but all sedate the patient while maintaining spontaneous respirations. The ideal agent would have no effect of heart and lung function and wear off rapidly after the procedure is complete. CS is used in the ER for reduction of fractures and dislocation as well as LP. My personal preferred drug is Propofol. Despite the fact that this drug contributed to the death of Michael Jackson, it is safe and effective when used appropriately. In infants and young children, Ketamine may be used as an alternative to propofol.

Obese patients present a challenge in performing an LP and having conscious sedation. Ultrasound may aid the ER doc to find the anatomic guideposts that are hidden under adipose tissue. Severely obese patients are more likely to have respiratory compromise from CS because of the restriction of their body weight on their chest muscles and diaphragm.

In the northeast, where I work, summer is encephalitis season. Meningitis and SAH can occur at any time. The ER staff is ready and able to properly diagnose and treat patients with the headache that may be the BIG ONE.